1. Field of the Invention
The present invention relates to high power planar Lightwave circuit (PLC) optical transmission (Tx) module and Tx/reception (Rx) module, and more particularly, to high power PLC optical Tx module and Tx/Rx module that incorporates a laser diode (LD) generating an optical signal, a semiconductor optical amplifier amplifying the optical signal, and/or a photodiode converting the optical signal into an electrical signal on one PLC platform in order to provide high optical power in a passive optical network (PON) system.
2. Description of the Related Art
A time division multiple access (TDMA) PON method is a standardized subscriber data transferring method using a fiber to the home (FTTH) network.
In a TDMA PON system, a plurality of subscribers shares an optical signal of one wavelength to transfer data. In the TDMA PON system, the output optical power of an optical Tx module (an optical Tx module for an optical line termination (OLT)) should be sufficiently large to allow a large number of subscribers, for example, more than 128, to share an optical signal of one wavelength.
Methods of increasing the output optical power include a method of increasing the output optical power of a laser diode (LD), which is an optical output device contained in an optical Tx module, and a method of increasing the output optical power by amplifying an optical signal generated by the LD of the optical Tx module using an optical amplifier.
However, there are limitations to increasing the LD's output optical power. Moreover, the method of increasing the optical power by adding an optical amplifier increases the costs and the size of the optical Tx module.
FIG. 1 is a block diagram of a network of a PON system using a conventional optical Tx module. Referring to FIG. 1, the PON system includes an OLT 100, an optical waveguide 120, a splitter 140, and a plurality of optical network terminations (ONTs) 160 that serve as subscriber terminals.
In the PON system, an optical signal is transferred from the OLT 100, which serves as a base station to the plurality of ONTs 160.
An optical signal of one wavelength generated by the OLT 100 is input to the splitter 140 through the optical waveguide 120.
The splitter 140 receives the optical signal of one wavelength, and splits the received optical signal into a plurality of signals having the same wavelength but lower optical power according to the number of branches. The split optical signals having reduced optical power are transferred to the plurality of ONTs 160.
The splitter 140 splits an optical signal into a plurality of optical signals having reduced optical power, and the optical power loss increases in proportion to the branch number. An excessively large number of branches results in an extreme decrease in the optical power, which makes it difficult to perform normal communication in the PON system.
Accordingly, in the PON system, the number of the ONTs 160 connected to one OLT 100 is determined by the optical power output from the OLT 100, optical power loss caused by optical branches at the splitter 140, and a power budget of another optical link.
For example, the splitter 140 illustrated in FIG. 1 may be a 1×16 splitter. Assuming that optical power required for normal communication is 0 dBm, it is possible to communicate with low optical power of approximately −6 dBm in the case of a 1×2 splitter. On the other hand, when a 1×128 splitter is used, high optical power of +10 dBm is needed for normal communication. That is, an optical signal output from the OLT 100 requires sufficient optical power to overcome optical power loss caused by the number of branches of the splitter 140 in order to secure as many ONTs 160 per OLT 100 as possible.
FIG. 2 is a block diagram of a conventional optical Tx module that can obtain high optical power. Referring to FIG. 2, the OLT 100 requires an optical Tx module having an optical power of more than +10 dBm in order to accommodate the ONTs 160 having 128 subscriber terminals.
However, since the output power of a conventional optical Tx module does not exceed +2 dBm, an optical amplifier should be connected to an output terminal of the optical Tx module to obtain an optical power of more than +10 dBm.
As illustrated in FIG. 2, the conventional high power optical Tx module includes an optical generator 200 generating an optical signal of one wavelength, and an optical amplifier 240 amplifying the generated optical signal.
The optical generator 200 includes a laser diode (LD) converting an electrical signal into an optical signal and outputting the optical signal, and a monitor photodiode (mPD) monitoring the optical signal output from the LD.
The optical signal generated by the optical generator 200 propagates to the optical amplifier 240 through an optical waveguide 220.
The optical amplifier 240 includes a semiconductor optical amplifier (SOA) amplifying the optical signal generated by the optical generator 200.
An optical connector 210 connects the optical generator 200 to the optical cable 220, an optical connector 230 connects the optical waveguide 220 to the optical amplifier 240, and an optical connector 250 connects the optical amplifier 240 to the ONTs 160 of FIG. 1.
When constructing a subscriber network using the PON system, the cost of the PON system is determined by the number of ONTs 160 connected to one OLT 100. A PON system including 16 to 32 ONTs 160 connected to one OLT 100 is widely used due to the limited optical power of the optical Tx module within the OLT 100.
Accordingly, if a method of increasing the optical power of the optical Tx module within the OLT 100 is available, up to 128 ONTs can be accommodated instead of just 32 ONTs. In other words, in order to connect a large number of ONTs 160 to one OLT 100, the optical power of the optical Tx module within the OLT 100 should be increased.
As mentioned above, the optical power can be increased by adding an optical amplifier to the optical Tx module. However, when adding the optical amplifier to the optical Tx module, the costs and the size of the optical Tx module increase because the optical generator 200 and the optical amplifier 240 are separately packaged.